Resistance Training Enhances Skeletal Muscle Innervation Without Modifying the Number of Satellite Cells or their Myofiber Association in Obese Older Adults

Abstract

Studies in humans and animal models provide compelling evidence for age-related skeletal muscle denervation, which may contribute to muscle fiber atrophy and loss. Skeletal muscle denervation seems relentless; however, long-term, high-intensity physical activity appears to promote muscle reinnervation. Whether 5-month resistance training (RT) enhances skeletal muscle innervation in obese older adults is unknown. This study found that neural cell-adhesion molecule, NCAM+ muscle area decreased with RT and was inversely correlated with muscle strength. NCAM1 and RUNX1 gene transcripts significantly decreased with the intervention. Type I and type II fiber grouping in the vastus lateralis did not change significantly but increases in leg press and knee extensor strength inversely correlated with type I, but not with type II, fiber grouping. RT did not modify the total number of satellite cells, their number per area, or the number associated with specific fiber subtypes or innervated/denervated fibers. Our results suggest that RT has a beneficial impact on skeletal innervation, even when started late in life by sedentary obese older adults.

Voluntary resistance wheel exercise from mid-life prevents sarcopenia and increases markers of mitochondrial function and autophagy in muscles of old male and female C57BL/6J mice

“…The suppressed expression of Runx1 in female muscle by RWE in the present study accords with observations in humans, where long-term (5-month, 3 days/week) resistance training in 65–79-year-old men and women increased vastus lateralis muscle strength with a concurrent decrease in Runx1 and Chrng expression relative to baseline (or pre-training) levels [124]. …”

Molecular indicators of denervation in aging human skeletal muscle

“…In response to denervation, NCAM is expressed in the extrasynaptic region of the muscle fiber where it is not normally present in the adult, and it is believed to facilitate the process of reinnervation . Denervation occurs either due to the decay of α‐motoneurons at the spinal cord or due to a disturbance in the NMJ at the level of the muscle fiber itself. Previous reports on the prevalence of NCAM + muscle fibers in young healthy participants are conflicting, ranging from zero to <0.5% to 2.4% .…”

Moderate‐intensity aerobic exercise improves skeletal muscle quality in older adults

“…CD56/NCAM is indicative of denervation of myofibers and is elevated in old muscle compared to young, highlighting progressive denervation with aging. Resistance exercise decreases NCAM+ fibers, suggesting reinnervation of myofibers contributing to strength improvement, even in the absence of hypertrophy . However, the impact of AET on denervation of myofibers has been less explored.…”